We note that some searches for planetary companions to young stars [1]} as well as surveys for `planetary-mass' T-dwarfs in young stellar clusters [2]} have employed
differential-methane band imaging. In this technique [3]} two images of a target are taken, one in a filter that matches the \(1.7-\,\rm \mu m\)  \(\rm CH_4\)  band and one
which probes the entire H band. When the two images are differenced, methane-bearing objects stand out as they are dark in the \(\rm CH_4\)  filter.
Our conclusions here suggest that such techniques must be used with caution as methane may simply not yet be present in planetary-mass objects even at effective temperatures below 1000 K.
